This invention relates to ligand-receptor assays.
Ligand-receptor assay procedures have been known for some time. In such procedures a molecule or substance of interest (ligand) is bound or otherwise reacted with a receptor which is specific to the ligand of interest to form an identifiable or even a quantifiable product.
Often, the receptor is bound to a membrane. Thus, the reaction or binding between the receptor and the ligand of interest is localized at the membrane. When the receptor is bound to a membrane, the sample is allowed to incubate on the surface of the membrane for a sufficient time to allow the ligand to come in contact with and bind or react with the receptor. See, for example, U.S. Pat. No. 4,246,339. Alternatively, an absorbent pad is attached to one side of the membrane to which the receptor is bound. The capillary action of the absorbent pad draws the sample through the membrane and brings the ligand in contact with the receptor. See, for example, U.S. Pat. No. 4,727,019.
While the use of an absorbent backing pad has proven to have practical application, it is not without its limitations and disadvantages. The process can be slow, especially if relatively large samples are used or if the absorbent pad approaches its saturation point, even if only in the area immediately below the membrane. Absorbent pad devices can be impractically bulky if more than a few hundred microliters must be applied to the device. The void volume within the absorbent pad places a practical limitation on the amount of fluid which can be applied to the membrane and be quickly and successfully drawn through by the capillary action of the pad.
It is therefore desired to obtain a membrane bound, ligand-receptor assay system which can draw moderate to large volumes of sample through a membrane to which a receptor is bound. It is also desired that such a system be capable of drawing the sample through the membrane as quickly as possible.